[Docs] Add language identifiers to fenced code blocks (#28955)

Add language identifiers to code blocks

examples/tensorflow/text-classification/README.md

@@ -36,7 +36,7 @@ may not always be what you want, especially if you have more than two fields!
 
 Here is a snippet of a valid input JSON file, though note that your texts can be much longer than these, and are not constrained
 (despite the field name) to being single grammatical sentences:
-```
+```json
 {"sentence1": "COVID-19 vaccine updates: How is the rollout proceeding?", "label": "news"}
 {"sentence1": "Manchester United celebrates Europa League success", "label": "sports"}
 ```
@@ -69,7 +69,7 @@ README, but for more information you can see the 'Input Datasets' section of
 [this document](https://www.tensorflow.org/guide/tpu).
 
 ### Example command
-```
+```bash
 python run_text_classification.py \
 --model_name_or_path distilbert-base-cased \
 --train_file training_data.json \
@@ -101,7 +101,7 @@ README, but for more information you can see the 'Input Datasets' section of
 [this document](https://www.tensorflow.org/guide/tpu).
 
 ### Example command
-```
+```bash
 python run_glue.py \
 --model_name_or_path distilbert-base-cased \
 --task_name mnli \